The early stage of computerized adaptive testing (CAT) refers to the phase of the trait estimation during the administration of only a few items. This phase can be characterized by bias and instability of estimation. In this study, an item selection criterion is introduced in an attempt to lessen this instability: the D-optimality criterion. A polytomous unconstrained CAT simulation is carried out to evaluate this criterion's performance under different test premises. The simulation shows that the extent of early stage instability depends primarily on the quality of the item pool information and its size and secondarily on the item selection criteria. The efficiency of the D-optimality criterion is similar to the efficiency of other known item selection criteria. Yet, it often yields estimates that, at the beginning of CAT, display a more robust performance against instability. (Contains 7 figures and 1 table.)